Esters of decahydronaphthalene dimethanol



United States Patent 3,172,897 ESTERS 0F DECAHYDRONAPHTHALENE Thisinvention relates to new and useful improvements in high-temperaturesynthetic lubricants, and more particularly to a novel class of diestersof cyclo-aliphatic glycols. This class of esters is especially useful ashightemperature lubricants and these esters are characterized by thermaland oxidative stability.

In recent years, the need has arisen for thermaland oxidation-stablelubricants capable of withstanding severe conditions encountered injetand rocket-propelled aircraft, missiles, and automotive gas turbines.A considerable amount of research has been done on synthetic lubricantssuch as esters, silicones, polyalkylene glycols, perfluorocarbons,halogenated hydrocarbons, silicate esters, and phosphate esters. Theserecent developments are reviewed in Review of Synthetic Lubricants, D.H. Moreton, Lubrication Engineering, April 1954, pages 65- 73, andSynthetic Oils Start Moving, Chemical and Engineering News, September 3,1956, pages 424M248. Among the numerous compounds tested for use aslubricants, the dibasic acid esters have been very promising due totheir lubricity, low volatility, low flammability.

The dibasic acid esters have received some attention forhigh-temperature use because of their thermal stability. However, in thepresence of any appreciable amount of air, dibasic acid esters, such asdioctyl sebacate, take up oxygen readily and are badly oxidized. Themonobasic esters are generally considered unsatisfactory as syntheticlubricants. Monobasic acid esters in general show relatively high wear,are volatile at elevated temperatures, and have relatively high pourpoints. Those which do not exhibit these weaknesses are not outstandingin lowtemperature characteristics and seem to be receptive to oxidativebreakdowns. Glycol diesters of monobasic acids have not been extensivelyinvestigated as synthetic lubricants, but tend to have rather poorlubricating properties, as well as being inferior in oxidative andthermal stability.

The properties which are sought in a high-temperature syntheticlubricant are:

(1) High viscosity index (VI),

(2) Low volatility,

(3) Low flammability,

(4) High thermal stability,

(5) High oxidation stability,

(6) High lubricity.

At present, none of the organic esters known to the prior art combineall of these desired properties.

A considerable amount of development work on organic esters and othersynthetic lubricants for use under high-temperature conditions has beencarried out at the Wright Air Development Center under the direction ofthe US. Air Force. The Department of Defense has developed a militaryspecification for synthetic-base lubricants for use in aircraft turbineengines. This specification, MIL-L-7808D, sets forth the requirementsfor synthetic lubricants for high-temperature use, and describes thevarious tests which a synthetic lubricant must pass to meet militaryspecifications.

It is therefore an object of this invention to provide a new andimproved synthetic lubricant which combines the properties of highlubricity, high thermal stability, high oxidation stability, lowflammability, low volatility,

and high viscosity index.

Another object of this invention is to provide a new and improvedsynthetic lubricant which meets the requirements of MilitarySpecification MILL7808D.

Another object of this invention is to provide a new and improvedorganic ester synthetic lubricant which combines high thermal andoxidation stability and high viscosity index.

A feature of this invention is the provision of a novel class of organicesters which are useful as high-temperature synthetic lubricants,combining properties of high lubricity, high thermal stability, highoxidation stability, low flammability, low volatility, and highviscosity index.

Another feature of this invention is the provision of a new class ofmonobasic esters of cycle-aliphatic glycols which are especially usefulas high-temperature lubricants.

Still another feature of this invention is the provision ofcycle-aliphatic glycol diesters which are useful as synthetic lubricantsand meet the requirements of Military Specification MIL-L-7808D.

Other objects and features of this invention will become apparent fromtime to time throughout the specification and claims as hereinafterrelated.

This invention is based upon our discovery that certain diesters ofcyclic glycols are especially stable against thermal breakdown andoxidation at elevated temperatures, and provide a combination ofdesirable lubricating properties including high viscosity index. Inparticular, this invention is based upon our discovery of a novel classof diesters of C C alkanoic (straight-chain or branchedchain) acids of C-C cycle-aliphatic glycols and C bicyclo-aliphatic glycols having sidechains with 1 to 10 carbon atoms therein. The esters of this inventionhave the general formula,

0 II It R COR R R O R where R is a C -C alkyl radical, R and R are C -Calkylene radicals (saturated divalent aliphatic hydrocarbon radicals)and R is a saturated C -C cyclo-alkylene radical or C bicyclo-alkyleneradical. These esters are prepared by esterification of cyclic glycolsof the formula, HOR R R OH, Where R R and R are as defined above, with CC alkanoic acids. The esterification is carried out by conventionalesterification methods, with or Without an esterification catalyst, asneeded, and using a diluent or an azeotrope-former, if desired. Cyclicglycols of the general formula which may be reacted with C C(straight-chain or branched-chain) alkanoic acids to produce the novelesters of this invention include the following:

ff (llHr CH-CH OH HOCHz-CH H CH2 CHa CH(CH2)IOOH HO(CH2)10 H CH;

CH, /CH: l-rocrr tllrr (IJHCmOH GE -CH2 /CH\gH/CH2 HOCH2?H CHz I /$HCH2OH CH2 H CH2 Alkanoic acids which may be reacted with the cyclicglycols include any of the straight-chain or branched-chain amass? C Cacids, e.g., hexanoic acid, n-octanoic acid, 2-ethylhexanoic acid,decanoic acid, lauric acid, palmitic acid, stearic acid, behenic acid,tricosanoic acid, etc.

The following non-limiting examples are illustrative of the scope ofthis invention.

Example I The di-Z-ethylhexanoate ester of 1,4-cyclohexanedimethanol wasprepared and evaluated for use as a hightemperature synthetic lubricant.1,4-cyclohexanemethanol was denuded of methanol by distillation and a569.3-g. portion of the purified material was charged with 100 cc. oftoluene (as solvent) to a 1-liter reaction flask, fitted with a refluxcondenser and a water trap. Then 528.8 g. of 2-cthylhexanoic acid and 3g. of p-toluene sulfonic acid (as esterification catalyst) were added,and the mixture was stirred and heated at reflux temperature until waterevolution ceased. The reaction mixture was then cooled, washed withwater until neutral to litmus, and dried over calcium sulfate.

Resulting ester was, purified by distillation at a pressure of 0.075 mm.Hg to an overhead temperature of 160 C., to remove the toluene andunreacted Z-ethylhexanoic acid. The physical properties of the esterwere as follows:

Acid number: 0.25

Carbon residue: Less than 0.1% Color (NPA): +3

Molecular weight (theon): 396 Molecular Weight (determined): 350 Flashpoint (COG): 430 F. Pour point: 65 F. or lower Viscosity (SUS), F.: 6000Viscosity (SUS) 100 F.: 117.2 Viscosity (SUS) 130 F.: 69.8 Viscosity(SUS) 210 F.: 39.9 Viscosity index: 63.

The 1,4 cyclohexane dimethyl-di(Z-ethylhexanoate) ester was evaluatedfor lubricant properties and found to meet the requirements of MilitarySpecification MIL-L- 7808B in all respects. The ester has a viscosity of4.99 centistokes at 210 F. and 24.3 centristokes at 100 F. Its flashpoint was 430 F. and it had a pour point of 65 F. or lower. A portion ofthe ester was heated to 500 P. (which is a more severe treatment thanthe 347 F. treatment required by MiL-L-780SD), and air was bubbledthrough it at a rate of about 5 liters per hour for 20 hours. Duringthis test, small squares of copper, steel and aluminum were placed inthe liquid being heated, and aerated. The liquid loss in weightresulting from this treatment was only 1.6% as compared to the loss of2.8% for a similar treatment of di-Z-ethylhexyl sebacate. The liquid hadan increase of 6% in viscosity at 130 F. and an increase of 21% inviscosity at 0 F. as a result of this treatment. When di-2-ethylhexysebacate was treated in this manner, the viscosity at 130 F. increased18% and the viscosity at 0 F. increased 35%. As a result of thistreatment, the acid neutralization number of the liquid increased fromsubstantially 0 to 18.9. This change in acid neutralization number isWithin the specifications of MIL-L-7 808D. The loss in weight of thecopper, steel, and aluminum squares in the liquid was within the valuesspecified by MILL7808D. This liquid has excellent lubricatingproperties, high viscosity index, high thermal and oxidative stability,and is useful for the lubrication of moving parts, e.g., gas turbineengines, throughout the temperature range from 0 to 600 F.

Exan'iple II v A one-moi portion of 1,3 cyclopentanedimethanol ischarged with 100 cc. of benzene to a 1-liter reaction flask fitted witha reflux condenser and a Water trap. Then 2.0

mols of Z-ethylhexanoic acid and 3.0 g. of p-toluene sulfonic acid(esterification catalyst) are added and the mixture stirred and heatedat reflux temperature until evolution of water has ceased. Finally, thereaction mixture is cooled, washed with Water until neutral to litmus,and dried over calcium sulfate. The ester is purified by vacuumdistillation to remove diluent benzene and unreacted materials. Theester which is obtained is a liquid having high viscosityindex, highoxidation and thermal stability, and good lubricating propertiesthroughout the temperature range of 0 to 600 F.

When 1,4-cyclohexanedimethanol is reacted with lauric acid or stearicacid in the same manner as described for Examples 1 and 2, the dilaurateor distearate ester is obtained. These esters have good lubricatingproperties, high thermal and oxidative stability and high viscosityindex. These esters are liquids over a wide temperature range and areuseful in the lubrication of high-temperature engines over a temperaturerange from 0 to about 600 Example III A one-moi portion ofdecahydronaphthalene dimethanol,

H2 is charged with 200 cc. of benzene to a 1-liter reaction flask fittedwith a reflux condenser and a water trap. Then, 2.0 mols of lauric acidand 3.0 g. of p-toluene sulfonic acid (catalyst) are added and themixture stirred and heated at reflux temperature until evolution ofwater has ceased. Finally, the reaction mixture is cooled, washed withwater until neutral to litmus, and dried over anhydrous calcium sulfate.The ester is purified by vacuum distillation to remove diluent benzeneand unreacted materials. The dilaurate ester which is obtained is aliquid having high viscosity-index, high oxidation stability, highthermal stability and good lubricating properties through out thetemperature range from 0 to 600 F.

While We have described our invention fully and completely with specialemphasis on several preferred embodiments thereof, we wish it to beunderstood within the scope of the appended claims this invention may beprac ticed otherwise than as specifically described herein.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An ester of the formula OH: H CH;

References Cited in the file of this patent UNITED STATES PATENTSSoloway et al Mar. 13, 1956 Staib et al. Mar. 13, 1956 Roelen et al.Dec. 24, 1957 Brannock Nov. 10, 1959 Pethrick et al. Oct. 24, 1961Craven Jan. 30, 1962 OTHER REFERENCES His-Kwei: Chemical Abstracts 52,154815 (1958). Liao et al.: I. Am. Chem. Soc. 77, 990-991 (1955).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,172,897 March 9, 1965 Charanjit Rai et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2, line 30, for "C -C read C C column 3,

line 42, for "centristokes" read centistokes line 56, for"di-Z-ethylhexy" read di-Z-ethylhexyl column 4, lines'2'4 to 29, forthat portion ofthe formula reading:

N I H read Signed and sealed this 3rd day of August 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. AN ESTER OF THE FORMULA